Cylinder head for engine

ABSTRACT

A number of embodiments of cylinder head constructions for internal combustion engines, wherein the intake and exhaust passages extend through the cylinder head and terminate in the respective upper and lower surfaces of the cylinder head so as to simplify machining. A number of variations and manifolding arrangements are also disclosed so as to permit the installation of the engine into an engine compartment and to provide a compact construction.

This application is a divisional of U.S. patent application No.08/438,502, filed May 10, 1995.

BACKGROUND OF THE INVENTION

This invention relates to a cylinder head for an engine and moreparticularly to an improved cylinder head porting arrangement andassociated manifold system for an internal combustion engine.

As is well know, engines normally have a cylinder block in which thecylinder bores are formed and a cylinder head which is detachableconnected to the cylinder block and which has surfaces or recesses thatcooperate with the cylinder bores to form the combustion chambers of theengine. With overhead valve engines, the intake and exhaust passages areformed in the cylinder head and extend from the combustion chambersurface in the sealing face of the cylinder head to external openings inthe cylinder head to which intake and/or exhaust manifolds areconnected. The cylinder head also has a valve chamber which is closed bya valve cover that is affixed to the cylinder head and which isremovable for servicing the valve mechanism and the camshafts, ifoverhead camshafts are employed. Hence, there are a number of surfaceson the exterior of the cylinder head which must be machined so as toimprove sealing.

Frequently, particularly with automotive applications, the intakepassages terminate on one side of the cylinder head and the exhaustpassages terminate on the other side of the cylinder head. The lowersurface must be machined to provide the sealing surface for the cylinderblock and the upper surface of the cylinder head must be machined toform the sealing surface for the valve cover. In addition, the surfacesaround the intake and exhaust passages where they exit the cylinder headalso must be machined so as to permit good sealing with the intake andexhaust manifold. Obviously, this requires complicated machiningoperations.

It is therefore, a principal object of this invention to provide animproved cylinder head arrangement for an internal combustion engine.

It is a further object of this invention to provide an improved cylinderhead arrangement for an internal combustion engine wherein the surfacesof the intake and exhaust passages which must be machined lie in thesame plane as the lower and upper sealing surfaces of the cylinder so asto facilitate and simplify machining operations.

With the induction system for an internal combustion engine, it is wellknown that the length of the induction system can be tuned to certainrunning conditions so as to provide optimum charging efficiency.Frequently this requires a long intake passage. However, when the engineis employed for powering a vehicle, such as an automobile, the spacedavailable in the engine compartment may not permit the use of longintake passages.

It is, therefore, a still further object of this invention to provide animproved compact induction system for an engine that permits theattainment of long lengths in relatively small volumetric areas.

In connection with the induction system for an engine, it is desirableto maintain a relatively straight unencumbered flow path to achieve highperformance and good volumetric efficiencies at wide-open throttleconditions. However, it is also desirable to induce turbulence in thecombustion chamber, particularly at low speed and low load conditions.There have been proposed types of flow control valves in the intakepassage of the cylinder head which can be utilized to permit lowrestriction under high speed, high load operation, and also theattainment of turbulence under low speed, low load conditions.

However, in order to be able to achieve this result, it is necessarythat the control valve be positioned relatively close to the intakeport. This presents certain problems, and can significantly complicatethe configuration of the cylinder head, if the flow control valve ispositioned directly in the cylinder head.

It is, therefore, a still further object of this invention to provide acompact cylinder head assembly wherein a flow control valve can bepositioned in the assembly but apart from the cylinder head, per se.

SUMMARY OF THE INVENTION

A first feature of the invention is adapted to be embodied in a cylinderhead for an internal combustion engine having a lower surface forsealing engagement with a cylinder block having a cylinder bore closedby the cylinder head lower surface to form a combustion chamber. Thecylinder head has an upper surface spaced from the lower surface andwhich surrounds a valve chamber and is adapted to be closed by a valvecover sealingly engaged with the upper surface. An intake passageextends through the cylinder head from an intake port in the combustionchamber to an inlet opening surrounded by a sealing surface that isco-planar with one of the upper and lower surfaces. An exhaust passageextends through the cylinder head from an exhaust port in the combustionchamber to an outlet opening surrounded by a sealing surface that isco-planar with the other of these surfaces.

Another feature of the invention is adapted to be embodied in a cylinderhead assembly for an internal combustion engine comprised of a cylinderhead having a lower surface for sealing engagement with a cylinder blockand having a cylinder bore closed by the cylinder head lower surface toform a combustion chamber. The cylinder head has an upper surface thatsurrounds a valve chamber and which is adapted to be closed by a valvecover sealingly engaged with the upper surface. A flow passage extendsthrough the cylinder head from the combustion chamber to the uppersurface. A cover is affixed to the cylinder head upper surface and has aflow passage that is aligned with the cylinder head flow passage. Thecover supports a flow control valve for controlling the flow through theflow passage.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a top plan view of a cylinder head constructed in accordancewith a first embodiment of the invention.

FIG. 2 is a cross-sectional view taken along the line 2--2 of FIG. 1 andshows the configuration of the intake passage of one cylinder of theengine.

FIG. 3 is a cross-sectional view taken along the line 3--3 of FIG. 1 andshows the exhaust passage of the other cylinder of the engine.

FIG. 4 is a cross-sectional view taken along the line 4--4 of FIG. 1.

FIG. 5 is a bottom plan view of the cylinder head.

FIG. 6 is a top plan view of a cylinder head with attached cam coverconstructed and intake manifold in accordance with a further embodimentof the invention.

FIG. 7 is an end view taken in the direction of the arrow 7 in FIG. 6.

FIG. 8 is a cross-sectional view taken along the line 8--8 of FIG. 6.

FIG. 9 is a partial cross-sectional view taken through a single cylinderof an engine constructed in accordance with another embodiment of theinvention.

FIG. 10 is a partially schematic top plan view of the embodiment of FIG.9.

FIG. 11 is a cross-sectional view taken through a single cylinder of anengine constructed in accordance with another embodiment of theinvention and shows how the engine may be mounted in the enginecompartment of a motor vehicle.

FIG. 12 is a cross-sectional view, in part similar to FIG. 11, and showsanother embodiment of the invention as positioned in a motor vehicleengine compartment.

FIG. 13 is a cross-sectional view, in part similar to FIGS. 11 and 12,and shows a still further embodiment of the invention.

FIG. 14 is a cross-sectional view, in part similar to the embodiments ofFIGS. 11-13, and shows another embodiment mounted in the enginecompartment of a motor vehicle.

FIG. 15 is a bottom plan view of a portion of the cylinder head showingthe combustion chamber recess constructed in accordance with anotherembodiment of the invention.

FIG. 16 is a view taken in a direction of the arrow 16 in FIG. 15 andshows how the intake and exhaust valves are placed in this embodiment.

FIG. 17 is a view, in part similar to FIG. 16, and shows another way inwhich the valves may be placed to arrive at a combustion chamberconfiguration and porting arrangement as shown in FIG. 15.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS OF THE INVENTION

Referring now in detail to the drawings and initially to the embodimentof FIGS. 1-5, a cylinder head constructed in accordance with thisembodiment of the invention is identified generally by the referencenumeral 21. The cylinder head 21 is formed as a casting from a lightweight material, such as aluminum or aluminum alloy. Of course, theparticular material from which the cylinder head 21 is cast is withinthe scope of those skilled in the art and generally forms no part of theinvention.

The cylinder head 21, in the illustrated embodiment, is designed for useeither in a two cylinder-engine or for one bank of a V-4 engine.Although the invention is described in conjunction with such a number ofcylinders and such alternative cylinder arrangements, it will be readilyapparent to those skilled in the art how the invention may be practicedwith engines having other numbers of cylinders and other cylinderorientation.

The cylinder head 21 has a lower surface 22 that is adapted to bebrought into sealing engagement with an associated cylinder block (notshown in these figures) and is affixed thereto in a known manner, as bythreaded fasteners which pass through openings 23 formed in the cylinderhead 21. Combustion chamber recesses 24 are formed in the cylinder headsurface 22 and are surrounded by portions of the surface 22 that are insealing engagement with the associated cylinder block or a cylinder headgasket interposed therebetween. The recesses 24 are comprised of a firstgenerally wedge-shaped portion 25 with squish areas 26 and 27 beingformed on opposite sides thereof.

In the illustrated embodiment, the cylinder head 21 is of atwo-valve-per-cylinder engine, although as should be readily apparent tothose skilled in the art, the features of the invention may be embodiedwith engines having multiple valves per cylinder.

An intake passage, indicated generally by the reference numeral 28,extends from the combustion chamber recess 24 and specifically an intakevalve seat 29 formed in registry with this recess to an upper surface 31of the cylinder head where it terminates in an inlet opening 32 that iscoextensive with the upper surface 31. An intake valve, indicatedgenerally by the reference numeral 33, is provided with a head portion34 which cooperates with the valve seat 29 for controlling the flowthrough the intake passage 28 from the inlet opening 32 to thecombustion chamber recess 24. A stem portion 35 of the intake valve 33is slidably supported within a valve guide 36 that is pressed or castinto the cylinder head casting 21.

A coil compression spring 37 encircles the upper portion of the valvestem 35 within a valve chamber 38 that is formed in the cylinder head21. The valve chamber 38 is surrounded by the upper cylinder headsurface 31. The surface 31 may, in a preferred form of the invention,extend generally parallel to the lower sealing surface 32.

The coil compression spring 37 acts against a keeper retainer assembly39 so as to normally urge the intake valves 33 to their closed position.The intake valves 33 are operated, for example, by means of an overheadcamshaft, which is mounted within the valve chamber 38 in a knownmanner. Later figures will show embodiments of how this can beaccomplished.

Referring now to FIG. 3, there are provided exhaust passages 41 whichalso extend through the cylinder head casting 21. The exhaust passages41 begin at exhaust valve seats 42 formed in the cylinder head recesses24 and which curve in a re-entrant fashion so as to exit the lowercylinder head surface 22 through an exhaust passage outlet opening 43.It will be seen that the outlet opening 43 is surrounded by the surface22 of the cylinder head and hence is coextensive with it.

Exhaust valves, indicated generally by the reference numeral 44, havehead portions 45 that cooperate with the exhaust valve seats 42 so as tocontrol the opening and closing of the exhaust passages 41. The exhaustvalves 44 have stem portions 46 that are slidably supported in valveguides 47 that are pressed or otherwise fixed in the cylinder headcasting 21. Coil compression springs 48 encircle the upper ends of theexhaust valve stems 46 that extend in the valve chamber 38. These valvesprings 48 act against keeper retainer assemblies 49 so as to urge theexhaust valves 44 to their closed position. The exhaust valves 44 areopened by the same camshaft, in a preferred form, that operates theintake valves 33. As noted above, this camshaft will be shown in laterfigures.

The exhaust outlet openings 43 are spaced .preferably transverselyoutwardly from the cylinder block and cooperate with an exhaust manifold(not shown in these figures) for collecting the exhaust gases anddelivering them to an appropriate exhaust system. Later embodiments willshow how this can be done. Since the surfaces surrounding the exhaustoutlet openings 43 are coplanar with the cylinder head sealing surface22, and in fact may form an extension of it, they can be easilymachined.

In a like manner, a cam cover (not shown) sealingly engages the uppercylinder head surface 31 for enclosing the valve chamber 38. An intakemanifold (not shown in these figures) may cooperate with the intakepassages 28 and specifically their inlet openings 32 for delivering anair and/or fuel charge to these intake passages 28. This intake manifoldmay be separate from the cam cover or, in some instances, may be formedin part by it, as will be described in conjunction with laterembodiments.

The side of the cylinder head casting 21 opposite to the exhaustpassages 41 is provided with pairs of spark plug receiving openings 51,each aligned with a respective one of the intake valves 33 and exhaustvalves 44 for each cylinder. Spark plugs are received in these recessesand are fired in a known manner by a suitable ignition system. Ofcourse, although two spark plug recesses 51 are illustrated, eithersingle spark plug recesses or greater numbers may be provided, dependingupon the particular design.

The cylinder head 21 is adapted to be employed in conjunction with acylinder block of any known type, and later embodiments will illustratehow the cylinder head 21 can be employed with various types of cylinderblocks. In addition, the cylinder head 21 is provided with a liquidcooling jacket through which coolant is circulated. Unlike conventionalengines, however, the cylinder head casting 21 is provided with a firstseries of intake cooling jackets 52 which surround and primarily servethe intake passages 28. These intake passage cooling jackets 52 receivewater from the cylinder block cooling jacket through a plurality ofopenings 53 that are formed in the lower cylinder head surface 22.

In a like manner, the exhaust passages 41 are provided with respectiveexhaust cooling jackets 54 which primarily encircle the exhaust passages41. These exhaust cooling jackets 54 receive coolant from the cylinderblock cooling jacket through passages 55 formed in the surface 22 andwhich are spaced from the inlet passage coolant openings 53. Byproviding relatively separate cooling jackets 52 and 54 for the intakepassages 28 and exhaust passages 41, respectively, it is possible tomaintain either a different effective temperature for the intakepassages than the exhaust passages of independent cooling. As a result,the intake passages 28 may be maintained at a lower temperature than ifthe coolant is mixed.

The rear end of the cylinder head 21 is provided with a boss 56 (FIG. 1)that has an exhaust coolant passage discharge opening 57 and an intakecoolant passage discharge opening 58. These openings 57 and 58communicate with a return passage (not shown) which may then mix thefluids at this point.

As has been noted, a cam cover, which may or may not form a portion ofthe intake manifold, is affixed to the cylinder head casting 21 inengagement with its sealing surface 31 to enclose the cam chamber 38.FIGS. 6-8 show a specific embodiment of the invention wherein such a camcover is employed, and it is identified generally by the referencenumeral. 61. Since the cylinder head 21 is of the type previouslydescribed, it is only shown partially in FIG. 8 and where components arethe same, they have been identified by the same reference numerals andwill not be described again, except insofar as is necessary tounderstand the construction and operation. Since the cam cover 61functions to provide a portion of the induction system, thecross-sectional view of FIG. 8 is taken through one of the intakepassages 28. Therefore, this view is generally similar to that of FIG.2, but shows, as noted, the cam cover arrangement.

It should be noted that the cam cover 61 has a lower surface 62 that isbrought into sealing engagement either with the cylinder head uppersurface 22 or an interposed gasket. Openings 63 formed in the cam cover64 and cylinder head casting 21 accommodate fasteners for affixing thecam cover 61 in place, In this position, it will be seen that the valvechamber 38 is closed.

The cam cover 61 is provided with a pair of intake passages 64 whichhave outlet openings 65 that register with the inlet openings 32 of thecylinder head intake passages 28 so as to provide a smooth flow passagetherebetween.

An intake manifold assembly, indicated generally by the referencenumeral 66, is detachably affixed to a surface 67 of the cam cover 61through which the inlet openings 64 pass. The manifold 66 has runnersections 67 that define passages 68 that communicate with the cam coverintake passages 64 and, accordingly, with the cylinder head intakepassages 28.

A plenum chamber 69 having an internal volume 71 serves the manifoldrunner passages 68. An atmospheric air inlet opening (not shown) isformed at the front side of the plenum chamber 69 and communicates withthe atmosphere through an air inlet device in which a throttle valve maybe positioned for controlling the engine speed.

The cam cover 61 is provided with bosses 72 adjacent its intake passageportion 64 which may be drilled and, if desired, tapped so as to receivefuel injectors (not shown) that spray fuel into the cam cover intakepassages 64 for distribution to the combustion chamber recesses 24 ofthe cylinder head 21 through its intake passages 28. A longitudinallyextending fuel manifold 73 can be formed integrally in the cam cover 61and terminates in an inlet opening 74 formed in a flange 75 formed atthe rear face thereof. Hence, this arrangement eliminates the necessityof providing separate fuel rails for delivering fuel to the fuelinjector.

The flange 75 may also be provided with water discharge or inletpassages 76 and 77 which communicate with the intake and exhaust coolantjacket outlet openings 58 and 57, respectively, of the cylinder headboss 56 so as to eliminate additional external fittings.

Although, from the foregoing description, it is believed that thoseskilled in the art can readily understand how the cylinder head 21 andcam cover 61 may be employed in conjunction with any type ofconventional engine structure, FIGS. 9 and 10 show a further embodimentof the invention wherein the entire portion of the engine, except forthe lower crankcase member and exhaust manifold, are depicted. Thisembodiment also shows how the cam cover 61, and specifically its intakepassages 64, may incorporate flow controlling throttle valves.

This structure will now be described by particular reference to FIGS. 9and 10, and in these figures, components which are the same as thosepreviously described or substantially the same have been identified bythe same reference numerals and will not be described again, exceptinsofar as is necessary to understand the construction and operation ofthis embodiment. Also, since the construction deals primarily with theintake side, the cross-sectional view of FIG. 9 corresponds to thecross-sectional views of FIGS. 2 and 8 and is taken through the cylinderhead intake passages 28.

In FIG. 9, a cylinder block 81 is show partially and in cross-section.This cylinder block 81 has cylinder bores 82 that are aligned with thecylinder head recesses 24. Pistons 83 reciprocate in the cylinder bores82 and are connected by means of piston pins 84 to the upper or smallends of connecting rods 85. The lower ends of the connecting rods 85 arejournaled on the throws 86 of a crankshaft, indicated generally by thereference numeral 87, in a known manner. The crankshaft 87 rotates in acrankcase chamber 88 that is closed by a crankcase member (not shown)that is detachable affixed to a skirt 89 of the cylinder block 81.

The cylinder block 81 has an upper sealing surface 91 that is eithersealingly engaged with the cylinder head lower surface 22 around thecylinder bores 82 or a gasket interposed therebetween.

This figure also shows the camshaft, indicated generally by thereference numeral 92, which is journaled in the cam chamber 58 foroperating the intake and exhaust valves 33 and 44, as aforedescribed.The camshaft 92 has spaced bearing portions that are journaled onbearing surfaces formed adjacent the cylinder head upper surface 31 andbearing caps 93 that are affixed thereto in a known manner. The camshaft92 has cam lobes 94 that cooperate with thimble tappets 95 for actuatingthe valves 33 and 44 in a well known manner.

This figure also shows the spark plugs 95 that are mounted in thecylinder head openings 51 and which have their spark terminals connectedto conductor terminals 96 in a well known manner.

Furthermore, this view also shows how the cam cover fuel injector bosses72 are machined so as to receive fuel injector sockets 97 that receivefuel injectors for injecting fuel into the cam cover intake passages 64and the intake passages 28 of the cylinder head 21.

From the construction of the cylinder head 21 and its cooperating camcover 61, it should be apparent that the resulting induction systemprovides very high charging efficiency. In addition, the configurationpermits the length of the intake passages to be tuned so as to obtainoptimum performance. However, this high efficiency intake system canresult in poor performance at low speeds and low loads due to the slowvelocity at which the charge enters the combustion chamber under theseconditions.

Therefore, these figures shows another arrangement wherein a flowcontrol valve assembly, indicated generally by the reference numeral 98,may be incorporated into the cam cover 61. This flow control valvearrangement 98 includes butterfly-type control valves 99 having acut-out configuration, as shown in FIG. 10. Because of thisconfiguration, when the control valves 99 are in a closed position, asshown in FIGS. 9 and 10, the intake charge flowing through the cam coverintake passage 64 and the cylinder head intake passage 28 will bedirected toward one side of the intake valve seat 29 and in a directionso as to generate not only a swirl around the axis of the cylinder bores82 but also a tumble action therearound. Of course, the degrees of swirland/or tumble can be controlled by controlling the shape of the controlvalves 99. Thus, by closing the control valves 99 the control valveassembly 98, under some running conditions, then a higher velocitycharge will flow into the combustion chambers, and the desired motioncan be achieved so as to increase turbulence and improve combustionunder these running conditions.

The control valves 99 are affixed to a common control valve shaft 101that is journaled in the cam cover 61 and which has a servomotor (notshown) affixed to one end thereof for appropriately positioning thecontrol valves 99.

Also, since the control valves 99 are provided in the cam cover 61, thecylinder head can be made simpler and also the control valves 99 can bepositioned closer to the valve seats 29 than when they are positionedexternally in a separate valve body that is affixed to the cylinder head21.

As has been noted, the configuration of the intake and exhaust passagespermitted by this cylinder head construction permits a fairly compactintake and exhaust system and yet one which can have sufficient lengthso as to provide the desired tuning. This has particular utility inconjunction with utilization in automotive applications or otherapplications wherein the engine is provided in an area that has limitedspace, and FIGS. 11-14 show a number of different embodimentsillustrating primarily how the arrangement can be employed in a motorvehicle.

Referring to the first of these embodiments as shown in FIG. 11, anengine, indicated generally by the reference numeral 151, having ageneral configuration of the type already described, is illustrated inan engine compartment 152 formed by a vehicle body 153. In thisembodiment, the engine compartment 152 is formed at the front of thevehicle with the front and rear directions being indicated by the arrowsF and R. Obviously rear engine placement is also possible.

The engine 151 is positioned so that the crankshaft 87 rotates about anaxis that is disposed transverse to the longitudinal center line of thevehicle having the body 153. This arrangement is particularly useful inconjunction with front wheel drive vehicles. However, it should be alsoapparent that the arrangement could be utilized with a rear engine, rearwheel drive arrangement.

In this embodiment, a cam cover 152 is affixed to the cylinder headassembly 21 and a separate intake manifold 153 is employed which isformed independently of the cam cover 152. This intake manifold 153 hasa plurality of runner sections 154 which have a generally inverted Ushape and which extend downwardly adjacent a side of the cylinder block81 and terminate in a plenum chamber 155 that has an atmospheric airinlet. It should be seen that the axes cylinder bores 82, indicated bythe line L, is disposed at an offset angle from the vertical and towardthe horizontal axis X to the rear of the engine compartment 152. Thispermits a compact engine compartment and a low hoodline whilemaintaining a long intake track.

In this figure, there is also depicted an exhaust manifold 156 whichcollects the exhaust gases from the cylinder head exhaust passages 41and delivers them to a catalytic converter 157 that is disposed to therear of the engine crankcase 88 which is formed, as aforenoted, by thecylinder block skirt 89. In addition, this figure shows the crankcasemember 158 affixed to the cylinder block skirt 89 so as to complete thecrankcase chamber 88. A suitable atmospheric exhaust system delivers theexhaust gases from the catalytic converter 157 to the atmosphere. Thisarrangement also permits the catalytic converter 157 to be positionedquite close to the combustion chambers 24 and thus improves itsoperating efficiency.

FIG. 12 shows another embodiment of the invention which is generallysimilar to the embodiment of FIG. 11, but permits the engine 151 to becanted even further toward the horizontal plane X. The cylinder boreaxis is canted in a plane M which is greater than that previouslydescribed. This is accomplished by reversing the cylinder head 21 on thecylinder block so that the exhaust manifold 156 and catalytic converter157 is disposed to the front of the engine. Thus, the relatively higherintake manifold runners 154 can have greater height.

FIG. 13 is another embodiment which is generally similar to theembodiment of FIG. 12, in that the induction system, indicated in thisembodiment by the reference numeral 201, is disposed rearwardly.However, rather than having the re-entrant portion, the manifold runners202 extend generally horizontally in line with the body portion 153 andterminate in a rearwardly positioned plenum chamber 203. This opens upthe space next to the engine 151 for various accessories driven from theengine crankshaft 87, such as a power steering pump 204, alternator 205,and air conditioning compressor 206. As a result of this arrangement,the engine not only provides maximum space utilization, but there is nosacrifice in the configuration and tuning of the intake and exhaustsystems.

In all of the embodiments previously described, the intake manifold andexhaust manifold have been disposed on opposite sides of the engine.However, other arrangements are also possible, and FIG. 14 shows anengine, indicated generally by the reference numeral 251, where theexhaust and intake manifolds are both positioned on the rear side of theengine in the engine compartment. In this embodiment, the engine is alsodisposed so that the axis of the cylinder bores 82 lies along thevertical Y axis. The intake system includes an intake manifold,indicated generally by the reference numeral 252, that has runnersections 253 which extend from the cylinder head intake passages 28upwardly and then rearwardly across the top of the engine to terminatein downwardly extending portions 254 that communicate with the plenumchamber 255. Hence, the plenum chamber 255 is disposed over the exhaustmanifold 157 and catalytic converter 158. A heat baffle 256 may bedisposed therebetween so as to provide heat insulation of the inductionmanifold 252 from the exhaust system, and specifically the catalyticconverter 158.

In all of the embodiments as thus far described, the intake and exhaustvalves 33 and 44 have been disposed so that the axes of reciprocationdefined by their respective stem portions 35 and 46 lie in a commonplane. This results in the side-by-side placement of the intake andexhaust valve seats 29 and 42, as shown in FIG. 5. This somewhat reducesthe maximum size which the valve head portions 34 and 45 may have. FIGS.15 and 16 show an embodiment wherein there is a stagger between thevalves so as to provide a potential of a larger valve size. In thisembodiment, it should be noted that the stems 35 and 46 intersect at theaxis of rotation of the camshaft 92.

FIG. 17 shows another embodiment wherein the axes of reciprocation ofthe intake and exhaust valves 33 and 44 are maintained parallel, but theaxes are offset at a distance d from each other. With this arrangement,it is still possible to employ a single camshaft 92 for operating boththe intake and exhaust valves 33 and 34, but the shape of their lobesmust be changed to accommodate the offset.

It should be readily apparent from the foregoing description that thedescribed embodiments of the invention provide a relatively simplecylinder head structure wherein machining of the surfaces surroundingthe intake and exhaust passages is on the same surface as the upper andlower surfaces of the cylinder head. This reduces setup time and hasother advantages as aforenoted. Of course, the foregoing description isthat of preferred embodiments of the invention, and various changes andmodifications may be made without departing from the spirit and scope ofthe invention, as defined by the appended claims.

We claim:
 1. A cylinder head assembly for an internal combustion enginecomprised of a cylinder head having a lower surface for sealingengagement with a cylinder block having a cylinder bore closed by saidcylinder head lower surface to form a combustion chamber, said cylinderhead having an upper surface surrounding a valve chamber adapted to beclosed by a valve cover sealingly engaged with said upper surface, anintake passage extending through said cylinder head from an intake portin said combustion chamber to an inlet opening surrounded by a sealingsurface coplanar with said upper surface and sealingly engaged by saidvalve cover, an intake passage formed in said valve cover cooperatingwith said cylinder head intake passage, and a flow-controlling valvepositioned in said valve cover for controlling the flow through saidvalve cover and said cylinder head intake passages.
 2. The cylinder headassembly of claim 1, wherein the cylinder head is provided with aplurality of intake passages and the valve cover has a plurality ofintake passages, each cooperating with a respective one of the cylinderhead intake passages.
 3. The cylinder head assembly of claim 2, whereinthe control valves comprise butterfly type valves all affixed to acommon valve shaft journaled within the cam cover.